What has stopped the perovskite solar cell from exiting the confines of scientific laboratories and becoming a viable choice for mass installations? For years, the reason behind stalled progress had little to do with light absorption. Instead, defects, phase instabilities, and degradation rates became a major obstacle for the widespread adoption of perovskites. What makes this particular breakthrough by scientists from Korea University, University of Toledo, and Seoul National University especially interesting is not only a new high-efficiency result. Rather, the authors managed to create a perovskite that better resembles the ideal material sought by engineers through many years of research.
In their paper recently published in Nature Energy, the scientists managed to reach a record-high 26.25% efficiency as well as demonstrate over 24,000 hours of operation during lab-accelerated testing. The innovation in their approach was the introduction of the 2D halide perovskite in contact with the conventional 3D perovskite absorber film, with thermal annealing employed to promote crystal growth at the interface between both. In fact, interface defects are precisely the weak point that has always been a major factor in device degradation.
However, the findings of the researchers went further than just a higher efficiency number. As it turns out, even placing the two perovskites together without any subsequent thermal treatment resulted in noticeable modifications in optical properties of the 3D layer. Speaking about the discovery, Jun Hong Noh noted, “Interestingly, these changes were reversible and strongly dependent on the organic cation.” Moreover, as soon as the scientists learned that the process led to a modification in phase transition within the 3D perovskite, “we were genuinely excited.”
This shift in attitude towards perovskite materials reflects the recent trends in the field of solar power production, with scientists focusing on interfaces, passivation, and stable architectures rather than creating ever more efficient cells. For instance, recently developed tandem devices employing silicon as the bottom layer along with perovskite cells above them achieved up to 35.0% certified efficiency, while industrial solutions proved capable of using a bilayer passivation of the interfaces to reach unprecedented levels of performance.
Still, there was one common denominator in almost all of the reviews of the field the issue of durability. While silicon-based perovskite cells have seen tremendous leaps in performance in the past few years, longevity remains their weakest point, making the stability improvements especially valuable. In turn, that is precisely where the study carried out by the scientists from Korea takes its relevance.
Namely, they applied thermal processing to promote lattice crystallization, resulting in improved parameters and phase stability in the FAPbI₃ composition known for strong photoelectric characteristics. Moreover, previous studies have demonstrated that similar application of 2D layer capping technology could lead to notable improvements in other designs, such as organic perovskite cells that retain more than 80% efficiency for 1,000 hours in 85°C atmosphere or inorganic cells with over 90% performance after 900 hours of ambient storage.
Consistency across different perovskite types would be the key. While silicon remains the gold standard when it comes to industrial applications due to its high reliability, efficiency ceiling of current top-end cells is rapidly approaching 26% to 27%, with tandems and multiple junctions reaching over 30% efficiency in silicon-perovskite stacks. For the latter to become anything more than the object of scientific interest, however, they need to solve the issue with stability at interfaces.